Several medical applications use ultrasonic energy. For example, U.S. Pat. Nos. 4,821,740, 4,953,565 and 5,007,438 disclose the use of ultrasonic energy to enhance the effect of various therapeutic compounds. An ultrasonic catheter can be used to deliver ultrasonic energy and a therapeutic compound to a treatment site within a patient's body. Such an ultrasonic catheter typically includes an ultrasound assembly configured to generate ultrasonic energy and a fluid delivery lumen for delivering the therapeutic compound to the treatment site.
As taught in U.S. Pat. No. 6,001,069, ultrasonic catheters can be used to treat human blood vessels that have become partially or completely occluded by plaque, thrombi, emboli or other substances that reduce the blood carrying capacity of the vessel. To remove or reduce the occlusion, the ultrasonic catheter is used to deliver solutions containing therapeutic compounds directly to the occlusion site. Ultrasonic energy generated by the ultrasound assembly enhances the effect of the therapeutic compounds. Such a device can be used in the treatment of diseases such as peripheral arterial occlusion, deep vein thrombosis or acute ischemic stroke. In such applications, the ultrasonic energy enhances treatment of the occlusion with therapeutic compounds such as urokinase, tissue plasminogen activator (“tPA”), recombinant tissue plasminogen activator (“rtPA”) and the like. Further information on enhancing the effect of a therapeutic compound using ultrasonic energy is provided in U.S. Pat. Nos. 5,318,014, 5,362,309, 5,474,531, 5,628,728, 6,001,069, 6,210,356 and 7,341,569.
Another use for ultrasonic catheters is in the treatment of pulmonary embolisms. Pulmonary embolisms (“PE”) are caused when a large blood clot obstructs the major blood vessels leading from the heart to the lungs. The victim's heart can be suddenly overwhelmed, with the task of pushing blood past this obstruction. About 5% of PEs are classified as massive and can result in rapid heart failure, shock and death without immediate therapy. Such massive PEs have traditionally been treated by a large dose of clot-dissolving drug (i.e., a thrombolytic). However, such treatment can result in unintended bleeding and even fatalities. Up to 40% of PEs are less critical obstructions, often called sub-massive PE. Current treatment protocols include treatment with anti-coagulant medication. Such treatments do not remove the clot but simply prevent the clot from growing larger. Recent studies suggest that failure to remove these sub-massive clots may have long-term adverse consequences including recurrent PE, chronic pulmonary hypertension and death.